The present invention relates in general to respirators and in particular to a new and useful closed circle respirator having an oxygen supply with an emergency passage for oxygen and control valve for that passage.
Respirators operating with an electric control on the cycle or rebreather principle make it possible to maintain the oxygen in the cycled breathing air at a desired normal percentage of about 21% independently of the surrounding pressure, e.g. when used as diving equipment. But it must be assured that the user of the equipment can safely continue to work also in case the electric breathing gas control should fail or that he can at least retreat to the safety of his starting base.
In a known closed cycle backpack respirator, the oxygen partial pressure in the cycle is maintained at a desired value by an electronic oxygen regulator.
In a first form of this device, the cycle comprises a breathing connection with mouthpiece and one-way valves for two breathing bags, namely one each on the inhaling and exhaling sides, which are connected together via a CO.sub.2 absorption cartridge. Feeding of the required oxygen is effected from a pressure gas bottle through a parallel connection of a throttle adjustable with a handwheel and a solenoid valve, which is closed in the inoperative state, on the entrance side of the absorption cartridge. An electro-chemical oxygen sensor is provided on the exit side of the absorption cartridge and regulates the oxygen partial pressure in the cycle to an adjustable nominal value via an electronic control device and the solenoid valve connected therewith. The measured value of the oxygen partial pressure is visible on an indicator which is worn on a wristband. The adjustable throttle is set so that it assures the minimum oxygen requirement needed for the user's survival. The normal consumption is then replenished via the solenoid valve.
In a second form, the replenishment of the consumed oxygen is effected via a series arrangement of a fixed throttle and a solenoid valve which is actuated by the control device and is open in the inoperative state, into the breathing bag located on the inhaling side. In case of breakdown, such as failure of the solenoid valve, an optical and/or acoustic warning signal is given when the signal of the sensor falls below a limit value. Then, through manual actuation of a switching device, the solenoid valve is by-passed and oxygen supplied continuously through the fixed throttle.
A disadvantage is that although an emergency supply is maintained in case of breakdown in the first form of the device, it is not sufficient for the normal requirement, as may be necessary also for retreat. Therefore, unless the failure is noticed by continuously watching the indicator, a dangerous oxygen depletion in the cycle may occur just the same. In the second form the device, manual switching is necessary in case of breakdown. This presupposes that the breakdown is recognized in time by watching the indicator or the alarm and that the user is then still able to act. (See U.S. Pat. No. 3,252,458).
In a known cycle apparatus, in particular for underwater work, the breathing gas, controlled by one-way flap valves, passes from a mixing chamber via a mouthpiece, which may perhaps be disposed also in a mask, to the user and thence via a breathing bag and a CO.sub.2 receiver back into the mixing chamber. A safety valve at the breathing bag relieves any overpressure in the surrounding medium. A gas bottle containing an inert gas-oxygen mixture is connected to the cycle via a pressure regulating valve and a pressure compensating valve as well as a possible, manually operated pushbutton valve. The cycle can thus be filled automatically or by hand. A second gas bottle containing oxygen is connected with the mixing chamber via a pressure regulating valve and a manually operated pushbutton valve. In parallel with the pushbutton valve, a solenoid disconnect valve and a solenoid valve, which are actuated via an electric circuit, are arranged in series. The circuit is connected with two sensors disposed in the mixing chamber, one of which picks up the total pressure and the other the oxygen partial pressure. The circuit arrangement of the circuit indicates the measured values on display devices which are worn on a wristband. The arrangement of the circuit further regulates the oxygen supply by actuation of the solenoid valve in such a way that selectively a constant partial pressure or a given percentage of oxygen is maintained in the cycle. If the oxygen partial pressure exceeds a limit value harmful to health, the circuit arrangement closes the solenoid disconnect valve until the oxygen value drops again, and it indicates overshooting by the flaring up of an alarm device. In addition, oxygen warning lamps inside the mask indicate whether the oxygen content is in the desired range or above or below it. For increased safety it is proposed to provide a second identical arrangement, in case a fault occurs in the first. As an additional monitoring device the measuring chamber contains a third sensor operating without outside energy which measures the oxygen partial pressure without connection with the circuit and indicates it on an independent gauge. In case of failure, the user can carry out by hand an emergency supply from the gas bottle containing inert gas-oxygen mixture via the two pushbutton valves.
The disadvantage is that despite complicated electronics and instrumentation the user is forced to recognize an occurring breakdown from observation of displays and signals and then to maintain an emergency supply while watching the displays by continued manual control operations which hinder him in the completion of his task or in his retreat. (see German No. OS 26 08 546).